UFH/Screed Expansion joints ?

[Post and beam]

Tuesday question, what is required to satisfy this? do i mount some kind of vertical MDF panel across the door jams at the height of the expected screed depth.(75mm in my case). Is it that simple?

[crispy_wafer]

something that can be cut or ground flat easily after the floor has dried out.  Also by doing this you may find the screed lips up a bit at the expansion joint, but again can be ground flat when the time comes.

[Post and beam]

Is it required at each door opening, and or anywhere else? I am thinking of a thin piece of say 6mm ply to screw a vertical bit of MDF to. This sits on top of the insulation/DPM separator layer

[crispy_wafer]

yes you could do, probably better than my effort as I used lengths of ufh expansion foam as had loads spare, just gave to the screeders to push into place when the screed was flowing. Screed both sides held it in position, not the most tidy, but it serves the intended purpose.

[JohnMo]

I did nothing, had one crack in floor, but wasn't at a door way.

[Mike]

9 hours ago, crispy_wafer said:

I used lengths of ufh expansion foam as had loads spare, just gave to the screeders to push into place when the screed was flowing. Screed both sides held it in position, not the most tidy, but it serves the intended purpose.

I've done similar, though using a plastic angle to keep them straight.

 

[Post and beam]

So where does this go please?

 

I have ordered some 8mm edge expansion foam because i was told that is the requirement. Cannot really understand why as there is either 25mm or 60mm kingspan around the perimeter everywhere.

[Russell griffiths]

I think you need to change your thoughts on the name of the joint. 
it’s not an expansion joint, but a movement joint. 
I was always told that if you have any shape like a tennis racket, so a big square area with a thin corridor coming off it, it will crack at the join between the two. 
I used a strip of firm foam with gaffa tape both sides, placed in every doorway, situated under where the door will close, so if you have different floor coverings in the different rooms the expansion trims will be hidden under the doors. 

[Post and beam]

Understand, so across the 'pinch' points as well as around the perimeter.

[saveasteading]

46 minutes ago, Post and beam said:

because i was told that is the requirement

I worry that you are getting such bad advice. What else don't they know?

 

17 minutes ago, Russell griffiths said:

not an expansion joint, but a movement joint

Correct.

Screed shrinks and cracks. It does not expand, yet people in the industry don't understand this basic fact.

@Post and beam

What are you doing and who is doing it?

 

 

[JohnMo]

29 minutes ago, saveasteading said:

It does not expand

I lined the edge of the screed (concrete) with 70mm of PIR and not the normal (crappy) expansion foam - got the normal sucking through teeth, your going to have issues.  So did the expansion calculation compared cooling (min temp) and heating at -9 outside (max temperature) and got to less than 1mm expansion over 25m (house length).

 

Think the issue is old house with UFH, they pump water at 50 degs on thin screed, so you get huge temperature swings. Then you can have issues. New house max flow is 35 or below, so very little temperature change in reality.

[Nickfromwales]

8 minutes ago, JohnMo said:

I lined the edge of the screed (concrete) with 70mm of PIR and not the normal (crappy) expansion foam - got the normal sucking through teeth, your going to have issues.  So did the expansion calculation compared cooling (min temp) and heating at -9 outside (max temperature) and got to less than 1mm expansion over 25m (house length).

 

Think the issue is old house with UFH, they pump water at 50 degs on thin screed, so you get huge temperature swings. Then you can have issues. New house max flow is 35 or below, so very little temperature change in reality.

Yup. Near to zero issue in real life with a decent performance house and a decent slab / emitter. Any movement we’ve anticipated has been mitigated with flexible tile adhesives, but still 1mm or so max over same distances, or less. 

As the slab and coverings heat up over time they tend to live together too, more relevant for porcelain / ceramics etc, so we don’t even put expansion / relief joints in any more.

 

Very different for thinner screeds as these are a bit more on/off ‘able and will perform differently I expect. How much more differently is down to flow temp and circumstances tbh.

 

We usually do 25-50mm PIR up stands plus the crappy expansion skirting; fitted only really to cover my arse as I work for 3rd parties.

[Tosh]

We just put the skirting foam around the internal walls, external is ICF so not required. For the cost and ease it does help stop any screed escaping if you have a rip in the membrane upstand for example.

If you want/need to put something in the doorways theres a couple of options. Just screw some ply/mdf/whatever it to one side of the door lining/studs and put the skirt foam over it so its easier to remove the ply afterwards then fill with expanding foam or just trim it down after the screed has poured.

 

Even if there were a few cracks then just accommodate it in the build up under the finish e.g. ditra/flexible adhesive

 

We had 140sqm 65mm gypsum, no joints - no cracks